LITHOCYSTIS. Ill 



V. LITHOCYSTIS. Allm. [Plate 14, B.] 



" Plant calcareous, consisting of a single plane of cellules, 

 which are disposed in radiating, dichotomous series, forming 

 an appressed, flabelliform frond." Allm. Name, from x<0oj, 

 a. stone, and xvn?, a bladder; because the cells have stony 

 coats. 



1. L. Allmanni, Harv. Phyc. Brit. t. clxvi. 



Parasitical on Chrysymenia clavellosa, from an oyster bed, Malahide, 

 Dublin, Professor Allman. Forming minute, dot-like patches of a whitish 

 colour on the fronds of the Chrysymenia. Each dot consists of one or se- 

 veral fan-shaped fronds, composed of quadrate cells, disposed in dichoto- 

 mous series. The plant is brittle, colourless, and effervesces in acid. 



ORDER X. DELESSERTACE^. 



Delesserieae, J. Ag. Alg. Medit. p. 116; Endl. 3rd Suppl. 

 p. 52 ; Lindl. Veg. King. p. 25. Gasterocarpeae (partim), 

 Due. Class, p. 65. Thamnophoreae (partim), Due. 1. c. p. 63. 

 Delesserieae and Plocameae, Kutz. Phyc. Gen. pp. 44, 449. 



DIAGNOSIS. Rosy or purplish red, or blood-red sea-weeds, 

 with a leafy, or rarely filiform, areolated, inarticulate frond, 

 composed of polygonal cells. Leaves delicately membrana- 

 ceous. Fructification double ; 1, Conceptacles (coccidia] 

 external or half immersed, hemispherical, usually imperfo- 

 rate, containing, beneath a membranous pericarp, a tuft of 

 dichotomous filaments, whose articulations are finally changed 

 into spores. 2, Tetraspores in distinctly defined sort, either 

 scattered through the frond or placed in proper fruit-leaflets 

 or sporophylla. 



NATURAL CHARACTER. Root usually a conical disk, in 

 some Plocamia and in Hymenena much branched, composed 

 of many clasping fibres ; and occasionally the frond is at- 

 tached at intervals by disk-like roots, which issue from the 

 under side of the midribs, or from the tips of the leaves. 

 Frond rarely (Plocamium) linear, very narrow or filiform, 

 and much branched ; usually leafy, or expanded : in many 

 cases forming distinct leaves, of definite shape, with costa 

 and lateral nerves, in others consisting of leaf-like membranes 



